1. Field of the Invention
This invention relates to a process of making a copolymer of maleic anhydride and methyl vinyl ether, and, more particularly, to a defined process of making such copolymers in solution having an exceedingly high specific viscosity and at a high solids content.
2. Description of the Prior Art
Goertz, H. et al, in U.S. Pat. No. 4,952,558, described a process of making copolymers of maleic anhydride and methyl vinyl ether in isopropyl acetate as solvent, optionally in the presence of a crosslinking agent, by precharging the maleic anhydride in the solvent, and then metering in the methyl vinyl ether and initiator over tie into the thus-precharged reactor. The copolymerization took place in an open kettle at the boiling point of the solvent. However, only low molecular weights copolymers were obtained in this manner, ranging from a K-value of 48-98, in the working examples, although it was stated that copolymers having K-values of 10-150 were possible. When high molecular weight crosslinked copolymers were desired, it was suggested that both the maleic anhydride and methyl vinyl ether monomers could be taken initially, i.e. as a precharge for the kettle, although none of the examples reflect such conditions. The mole ratio of maleic anhydride to methyl vinyl ether in the process coincided substantially with the 1:1 copolymerization ratio of these monomers, with essentially no excess (less than 10%) of methyl vinyl ether being present. The result was a copolymer of low molecular weight as a solution of low solids content.
Kwak, Y. T. et al, in U.S. Pat. No. 5,874,510, described a related process for making crosslinked maleic anhydride-methyl vinyl ether copolymers by feeding molten maleic anhydride monomer into a precharged mixture of methyl vinyl ether and a crosslinker in isopropyl acetate. The rest of the methyl vinyl ether was fed as a separate stream along with the molten maleic anhydride.
However, neither of these processes are suitable for making copolymers of high specific viscosity and at a high solids content.
Accordingly, it is an object of this invention to provide a new and improved process for making uncrosslinked copolymers of maleic anhydride (MA) and methyl vinyl ether (MVE) monomers, the specific viscosity (SV) of the product being about 2.5-6, preferably 3-5, indicating a weight average molecular weight of substantially above one million, preferably above 1.5 million, as a solution in isopropyl acetate, and at a solids content of about 20-45%, preferably 30-40%, wherein the mole ratio of MA:MVE in the reaction mixture is 1:xe2x89xa71.5 to 1: less than 3, preferably about 1:2.4, and the free radical initiator is present in an amount of 0.02-0.3%, preferably 0.05-0.2%, based on total monomers.
A feature of this invention is a process of making copolymers of MA and MVE wherein part of MVE in isopropyl acetate (IPAc) is precharged into a reactor heated to about 50-90xc2x0 C., and then separate streams of (i) a solution of MA in IPAc, (ii) the rest of MVE, at the defined total mole ratio of MA:MVE, and (iii) a free radical initiator dissolved in IPAc, at a specified concentration, is introduced into the precharged reactor.
Another feature of the invention is the provision of MA-MVE copolymers of high specific viscosity as a powder.
These and other objects and features of the invention will be made apparent from the following more particular description of the invention.
What is described herein is a process for making a solution of a copolymer of maleic anhydride (MA) and methyl vinyl ether (MVE) monomers, the specific viscosity (SV) of the product being about 2.5-6, preferably 3-5, indicating a weight average molecular weight of substantially above one million, preferably above 1.5 million, and a solids content of about 20-50%, preferably 30-40%, in isopropyl acetate (IPAc), which comprises:
(a) precharging part, preferably half, of MVE in IPAc solvent into a reactor heated to about 50-90xc2x0 C., preferably 65-75xc2x0 C., and
(b) feeding (i) a solution of MA in IPAc, (ii) the rest of MVE, at a mole ratio of MA:MVE of 1:xe2x89xa71.5 to 1: less than 3, preferably 1:2.4 and (iii) a free radical initiator, preferably decanoyl peroxide, dissolved in IPAc, in an amount of 0.02-0.3%, preferably 0.05-0.2%, based on total monomers, into the reactor over time, preferably at least 30 minutes.
Suitably, (i), (ii) and (iii) are fed into the precharged reactor over a period of at least 30 minutes.
Powders of such MA/MVE copolymers are made by removing the solvent from the solution.
In suitable embodiments of the invention, the free radical initiator is an acyl peroxide, such as diacetyl peroxide, dibenzoyl peroxide and dilauryl peroxide; aperester, such as tert-butyl perpivalate, and tert-butyl per-2-ethylhexanoate; a peroxide, such as decanoylperoxide a di-tert-butyl peroxide; a percarbonate, such as dicyclohexyl peroxydicarbonate; and an azo compound, such as 2,2xe2x80x2-azobisisobutyronitrile, 2,2xe2x80x2-azobis-(2,4-dimethyl- valeronitrile), 1,1xe2x80x2-azobis-(l-cyclohexanecarbonitrile) and dimethyl-2,2xe2x80x2-azobis- (isobutyrate). A preferred initiator is decanoyl peroxide.